This invention relates to an electric motor driven tool, and more particularly, to a power tool including a speed reduction mechanism for changing the revolution speed of a tool.
In general, there is known a power tool in which the tool is driven by an electric motor through a gear speed reduction mechanism comprising a plurality of stages of planetary speed reduction mechanisms, such electric motor and speed reduction mechanisms being arranged in a tool body. The power tool further includes a trigger switch for carrying out "ON" or "OFF" switching operations of the motor. The tool is driven and rotated in a desired operation mode by operating the trigger switch.
In a conventional power tool of the character described above, the rotation speed of an output shaft of a gear speed reduction mechanism driven by an electric motor is switched from a low speed to a high speed or vice versa to thereby drive the tool with variable rotation speeds.
One example of such a power tool including a speed reduction mechanism is disclosed in Japanese Patent Laid-open Publications No. 61-209883 and No. 62-224584.
The speed reduction mechanism disclosed in these prior art references includes a slide gear member provided with an internal gear engaged with a plurality of planetary gears of the speed reduction mechanism. The slide gear member is disposed to be movable in its rotation axis direction and is supported to be rotatable or non-rotatable in accordance with its moved positions.
In a conventional power tool, an arcuate swing member is connected to such a slide gear member in a manner that the slide gear member can be moved by swinging the swing member by means of a speed change lever. Two kinds of speed reduction ratios can be obtained in accordance with the difference between the rotation speeds of the planet gears at both the rotation stop time of the slide gear member and the rotating time of the internal gear by the operation of the speed change lever, whereby a desired speed reduction operation can be performed.
In the conventional power tool of the described type, however, the slide gear member is moved by the swinging motion of the swing member, and moreover, since the swing member is formed so as to have an arcuate configuration, the swing member is subjected to an expansion deformation when a load is applied thereto. Thus, there causes a case in which the smooth motion of the slide gear member is not expected, resulting in less reliability of the speed changing operation. Furthermore, the requirement for the location of the speed change lever and the swing member will result in the increasing of the constructional members or parts as well as troublesome manufacturing workings thereof.